How much would it take to convince you to take a later or earlier train home to avoid rush-hour trains on the CTA Red Line jammed with Cubs fans headed to a night game at Wrigley Field?

Would a $2.25 rebate be enough? How `bout $5?

A fall pilot program tested the incentive idea and found that it managed to divert nearly 18 percent of Red Line traffic before night games at Wrigley.

A second rebate experiment is planned within the next three months, possibly for a Bulls game at the United Center or a Bears game at Soldier Field.

The Wrigley test was modestly publicized in August, using posters on Red Line trains. Daily commuters who volunteered for the pilot got text messages.

Texts sent Aug. 28, 29, 31 and Sept. 14 simply alerted riders of the Cubs night game and attempted to steer them to earlier or later trains likely to be less crowded.

Messages delivered on Aug. 30 and Sept. 12 offered a $2.25 rebate to riders’ Ventra cards if they steered clear of Red Line trains between 5 p.m. and 6 p.m. and chose to travel home an hour earlier or an hour later.

Sept. 13 texts offered a $5 charitable donation in the commmuter’s name to “Stand up to Cancer.” Messages sent Oct. 19 upped the ante to a $5 rebate.

Not surprisingly, fare rebates had the biggest impact on behavior among the 1,172 rebate-eligible commuters who registered.

Those givebacks triggered a 17.5 percent drop in ridership during the peak demand hour from 5-to-6 p.m. — from 193 riders using the six downtown Red Line stations to 159 commuters.

Informational alerts alone and charitable donations in the commuter’s name triggered a 9.7 percent diversion of traffic. But that was viewed as “not statistically significant.”

The incentive program was a partnership between City Digital, Mastercard, the CTA and ideas42, a behavioral-science research firm.

Brenna Berman is executive director of City Digital, an innovation lab on Goose Island that helps big cities experiment with solutions to urban challenges.

On Tuesday, Berman was in Spain to present the results — and the promise they hold for Chicago and other major cities — to the Smart City Expo World Congress.

“We’re looking for ways to help not just the CTA, but transit organizations all over the country, find affordable and relatively easy ways to smooth the demand for transit across all of the hours of operation,” Berman said by telephone from Barcelona.

“Supply-side solutions — building more transit lines, supplying more trains — are quite expensive and they can take a long time to deploy. What we’re doing is looking at ways that data can manage the demand-side for transit to address the issue of congestion by helping residents understand the better time to travel to really smooth the peaks and valleys of transit patterns.”

Berman was not at all surprised that “such a small incentive” managed to move the needle.

“We were only looking for a small change in behavior. … We were asking them to change how they commute home on this given day because of a Cubs game. It wasn’t a change to their commuting behavior every day. That, I think, would take a larger incentive. But that’s the kind of model that we’ll test in the future,” she said.

Ald. Tom Tunney (44th), whose ward includes Wrigley, was unaware of the rebate experiment and somewhat suspicious of the results.

“I use the trains during that hour. It’s as crowded as ever. I don’t know where they’re getting their numbers because it’s standing room only,” Tunney said.

“People are working harder than ever. They’re working longer than ever. They want to get home. They’re using the trains. They’re not using the buses. But, I don’t see a 17 percent reduction. I would notice that.”

Berman said other special events when rebates might be worthwhile include Lollapalooza and the annual lighting ceremony for Chicago’s official Christmas tree.

“If the CTA sees value in this sort of effort to smooth things out for their operations, hopefully they’ll be able to look at implementing this across the system to bring these kind of results to more events across the city and make things better for their riders,” Berman said.

Mastercard offers CTA Ventra cardholders the option of a opening a Mastercard debit account connected to the card. The company set aside $50,000 for the incentive program, but needed only $3,500 for the rebates and charitable donations.